function ret = lookuptable(grauwert, cumu_histo, num_pixels)
    cumu_histo = cumu_histo*num_pixels;
    c_min = 0;
    for i = (1:length(cumu_histo))
        c_min = cumu_histo(i);
        if c_min > 0
            break;
        end
    end
    ret = round(((cumu_histo(grauwert+1) - c_min)/(num_pixels - c_min)) * (length(cumu_histo)-1));
end